/* packet-image-jfif.c
 *
 * Routines for JFIF image/jpeg media dissection
 * Copyright 2004, Olivier Biot.
 *
 * $Id: packet-image-jfif.c 26308 2008-09-30 14:49:44Z wmeier $
 *
 * Refer to the AUTHORS file or the AUTHORS section in the man page
 * for contacting the author(s) of this file.
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * JFIF media decoding functionality provided by Olivier Biot.
 * 
 * The JFIF specifications are found at several locations, such as:
 * http://www.jpeg.org/public/jfif.pdf
 * http://www.w3.org/Graphics/JPEG/itu-t81.pdf
 *
 * The Exif specifications are found at several locations, such as:
 * http://www.exif.org/
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/* Edit this file with 4-space tabulation */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <glib.h>

#include <epan/packet.h>

/* General-purpose debug logger.
 * Requires double parentheses because of variable arguments of printf().
 *
 * Enable debug logging for JFIF by defining AM_CFLAGS
 * so that it contains "-DDEBUG_image_jfif" or "-DDEBUG_image"
 */
#if (defined(DEBUG_image_jfif) || defined(DEBUG_image))
#define DebugLog(x) \
	g_print("%s:%u: ", __FILE__, __LINE__); \
	g_print x
#else
#define DebugLog(x) ;
#endif

#define IMG_JFIF "image-jfif"

/************************** Variable declarations **************************/

#define MARKER_TEM		0xFF01

/* 0xFF02 -- 0xFFBF are reserved */

#define MARKER_SOF0		0xFFC0
#define MARKER_SOF1		0xFFC1
#define MARKER_SOF2		0xFFC2
#define MARKER_SOF3		0xFFC3

#define MARKER_DHT		0xFFC4

#define MARKER_SOF5		0xFFC5
#define MARKER_SOF6		0xFFC6
#define MARKER_SOF7		0xFFC7
#define MARKER_SOF8		0xFFC8
#define MARKER_SOF9		0xFFC9
#define MARKER_SOF10	0xFFCA
#define MARKER_SOF11	0xFFCB

#define MARKER_DAC		0xFFCC

#define MARKER_SOF13	0xFFCD
#define MARKER_SOF14	0xFFCE
#define MARKER_SOF15	0xFFCF

#define MARKER_RST0		0xFFD0
#define MARKER_RST1		0xFFD1
#define MARKER_RST2		0xFFD2
#define MARKER_RST3		0xFFD3
#define MARKER_RST4		0xFFD4
#define MARKER_RST5		0xFFD5
#define MARKER_RST6		0xFFD6
#define MARKER_RST7		0xFFD7

#define MARKER_FFDB		0xFFDB
#define MARKER_SOI		0xFFD8
#define MARKER_EOI		0xFFD9
#define MARKER_SOS		0xFFDA
#define MARKER_DQT		0xFFDB
#define MARKER_DNL		0xFFDC
#define MARKER_DRI		0xFFDD
#define MARKER_DHP		0xFFDE
#define MARKER_EXP		0xFFDF

#define MARKER_APP0		0xFFE0
#define MARKER_APP1		0xFFE1
#define MARKER_APP2		0xFFE2
#define MARKER_APP3		0xFFE3
#define MARKER_APP4		0xFFE4
#define MARKER_APP5		0xFFE5
#define MARKER_APP6		0xFFE6
#define MARKER_APP7		0xFFE7
#define MARKER_APP8		0xFFE8
#define MARKER_APP9		0xFFE9
#define MARKER_APP10	0xFFEA
#define MARKER_APP11	0xFFEB
#define MARKER_APP12	0xFFEC
#define MARKER_APP13	0xFFED
#define MARKER_APP14	0xFFEE
#define MARKER_APP15	0xFFEF

#define MARKER_JPG0		0xFFF0
#define MARKER_JPG1		0xFFF1
#define MARKER_JPG2		0xFFF2
#define MARKER_JPG3		0xFFF3
#define MARKER_JPG4		0xFFF4
#define MARKER_JPG5		0xFFF5
#define MARKER_JPG6		0xFFF6
#define MARKER_JPG7		0xFFF7
#define MARKER_JPG8		0xFFF8
#define MARKER_JPG9		0xFFF9
#define MARKER_JPG10	0xFFFA
#define MARKER_JPG11	0xFFFB
#define MARKER_JPG12	0xFFFC
#define MARKER_JPG13	0xFFFD

#define MARKER_COM		0xFFFE

#define marker_has_length(marker) ( ! ( \
	   ((marker) == MARKER_TEM) \
	|| ((marker) == MARKER_SOI) \
	|| ((marker) == MARKER_EOI) \
	|| ( ((marker) >= MARKER_RST0) && ((marker) <= MARKER_RST7) ) \
	) )


static const value_string vals_marker[] = {
	{ MARKER_TEM,	"Reserved - For temporary private use in arithmetic coding" },
	{ MARKER_SOF0,	"Start of Frame (non-differential, Huffman coding) - Baseline DCT" },
	{ MARKER_SOF1,	"Start of Frame (non-differential, Huffman coding) - Extended sequential DCT" },
	{ MARKER_SOF2,	"Start of Frame (non-differential, Huffman coding) - Progressive DCT" },
	{ MARKER_SOF3, 	"Start of Frame (non-differential, Huffman coding) - Lossless (sequential)" },
	{ MARKER_DHT,	"Define Huffman table(s)" },
	{ MARKER_SOF5,	"Start of Frame (differential, Huffman coding) - Differential sequential DCT" },
	{ MARKER_SOF6,	"Start of Frame (differential, Huffman coding) - Differential progressive DCT" },
	{ MARKER_SOF7,	"Start of Frame (differential, Huffman coding) - Differential lossless (sequential)" },
	{ MARKER_SOF8,	"Start of Frame (non-differential, arithmetic coding) - Reserved for JPEG extensions" },
	{ MARKER_SOF9,	"Start of Frame (non-differential, arithmetic coding) - Extended sequential DCT" },
	{ MARKER_SOF10,	"Start of Frame (non-differential, arithmetic coding) - Progressive DCT" },
	{ MARKER_SOF11,	"Start of Frame (non-differential, arithmetic coding) - Lossless (sequential)" },
	{ MARKER_DAC,	"Define arithmetic coding conditioning(s)" },
	{ MARKER_SOF13,	"Start of Frame (differential, arithmetic coding) - Differential sequential DCT" },
	{ MARKER_SOF14,	"Start of Frame (differential, arithmetic coding) - Differential progressive DCT" },
	{ MARKER_SOF15,	"Start of Frame (differential, arithmetic coding) - Differential lossless (sequential)" },
	{ MARKER_RST0,	"Restart interval termination - Restart with modulo 8 count 0" },
	{ MARKER_RST1,	"Restart interval termination - Restart with modulo 8 count 1" },
	{ MARKER_RST2,	"Restart interval termination - Restart with modulo 8 count 2" },
	{ MARKER_RST3,	"Restart interval termination - Restart with modulo 8 count 3" },
	{ MARKER_RST4,	"Restart interval termination - Restart with modulo 8 count 4" },
	{ MARKER_RST5,	"Restart interval termination - Restart with modulo 8 count 5" },
	{ MARKER_RST6,	"Restart interval termination - Restart with modulo 8 count 6" },
	{ MARKER_RST7,	"Restart interval termination - Restart with modulo 8 count 7" },
	{ MARKER_SOI,	"Start of Image" },
	{ MARKER_EOI,	"End of Image" },
	{ MARKER_SOS,	"Start of Scan" },
	{ MARKER_DQT,	"Define quantization table(s)" },
	{ MARKER_DNL,	"Define number of lines" },
	{ MARKER_DRI,	"Define restart interval" },
	{ MARKER_DHP,	"Define hierarchical progression" },
	{ MARKER_EXP,	"Expand reference component(s)" },
	{ MARKER_APP0,	"Reserved for application segments - 0" },
	{ MARKER_APP1,	"Reserved for application segments - 1" },
	{ MARKER_APP2,	"Reserved for application segments - 2" },
	{ MARKER_APP3,	"Reserved for application segments - 3" },
	{ MARKER_APP4,	"Reserved for application segments - 4" },
	{ MARKER_APP5,	"Reserved for application segments - 5" },
	{ MARKER_APP6,	"Reserved for application segments - 6" },
	{ MARKER_APP7,	"Reserved for application segments - 7" },
	{ MARKER_APP8,	"Reserved for application segments - 8" },
	{ MARKER_APP9,	"Reserved for application segments - 9" },
	{ MARKER_APP10,	"Reserved for application segments - 10" },
	{ MARKER_APP11,	"Reserved for application segments - 11" },
	{ MARKER_APP12,	"Reserved for application segments - 12" },
	{ MARKER_APP13,	"Reserved for application segments - 13" },
	{ MARKER_APP14,	"Reserved for application segments - 14" },
	{ MARKER_APP15,	"Reserved for application segments - 15" },
	{ MARKER_JPG0,	"Reserved for JPEG extensions - 0" },
	{ MARKER_JPG1,	"Reserved for JPEG extensions - 1" },
	{ MARKER_JPG2,	"Reserved for JPEG extensions - 2" },
	{ MARKER_JPG3,	"Reserved for JPEG extensions - 3" },
	{ MARKER_JPG4,	"Reserved for JPEG extensions - 4" },
	{ MARKER_JPG5,	"Reserved for JPEG extensions - 5" },
	{ MARKER_JPG6,	"Reserved for JPEG extensions - 6" },
	{ MARKER_JPG7,	"Reserved for JPEG extensions - 7" },
	{ MARKER_JPG8,	"Reserved for JPEG extensions - 8" },
	{ MARKER_JPG9,	"Reserved for JPEG extensions - 9" },
	{ MARKER_JPG10,	"Reserved for JPEG extensions - 10" },
	{ MARKER_JPG11,	"Reserved for JPEG extensions - 11" },
	{ MARKER_JPG12,	"Reserved for JPEG extensions - 12" },
	{ MARKER_JPG13,	"Reserved for JPEG extensions - 13" },
	{ MARKER_COM,	"Comment" },
	{ 0x00, NULL }
};

static const value_string vals_units[] = {
	{ 0, "No units; Xdensity and Ydensity specify the pixel aspect ratio" },
	{ 1, "Dots per inch" },
	{ 2, "Dots per centimeter" },
	{ 0x00, NULL }
};

static const value_string vals_extension_code[] = {
	{ 0x10, "Thumbnail encoded using JPEG" },
	{ 0x11, "Thumbnail encoded using 1 byte (8 bits) per pixel" },
	{ 0x13, "Thumbnail encoded using 3 bytes (24 bits) per pixel" },
	{ 0x00, NULL }
};

static const value_string vals_exif_tags[] = {
	/*
	 * Tags related to image data structure:
	 */
	{ 0x0100, "ImageWidth" },
	{ 0x0101, "ImageLength" },
	{ 0x0102, "BitsPerSample" },
	{ 0x0103, "Compression" },
	{ 0x0106, "PhotometricInterpretation" },
	{ 0x0112, "Orientation" },
	{ 0x0115, "SamplesPerPixel" },
	{ 0x011C, "PlanarConfiguration" },
	{ 0x0212, "YCbCrSubSampling" },
	{ 0x0213, "YCbCrPositioning" },
	{ 0x011A, "XResolution" },
	{ 0x011B, "YResolution" },
	{ 0x0128, "ResolutionUnit" },
	/*
	 * Tags relating to recording offset:
	 */
	{ 0x0111, "StripOffsets" },
	{ 0x0116, "RowsPerStrip" },
	{ 0x0117, "StripByteCounts" },
	{ 0x0201, "JPEGInterchangeFormat" },
	{ 0x0202, "JPEGInterchangeFormatLength" },
	/*
	 * Tags relating to image data characteristics:
	 */
	{ 0x012D, "TransferFunction" },
	{ 0x013E, "WhitePoint" },
	{ 0x013F, "PrimaryChromaticities" },
	{ 0x0211, "YCbCrCoefficients" },
	{ 0x0214, "ReferenceBlackWhite" },
	/*
	 * Other tags:
	 */
	{ 0x0132, "DateTime" },
	{ 0x010E, "ImageDescription" },
	{ 0x010F, "Make" },
	{ 0x0110, "Model" },
	{ 0x0131, "Software" },
	{ 0x013B, "Artist" },
	{ 0x8296, "Copyright" },
	/*
	 * Exif-specific IFD:
	 */
	{ 0x8769, "Exif IFD Pointer"},
	{ 0x8825, "GPS IFD Pointer"},
	{ 0xA005, "Interoperability IFD Pointer"},

	{ 0x0000, NULL }
};

static const value_string vals_exif_types[] = {
	{ 0x0001, "BYTE" },
	{ 0x0002, "ASCII" },
	{ 0x0003, "SHORT" },
	{ 0x0004, "LONG" },
	{ 0x0005, "RATIONAL" },
	/* 0x0006 */
	{ 0x0007, "UNDEFINED" },
	/* 0x0008 */
	{ 0x0009, "SLONG" },
	{ 0x000A, "SRATIONAL" },

	{ 0x0000, NULL }
};

/* Initialize the protocol and registered fields */
static int proto_jfif = -1;

/* Marker */
static gint hf_marker = -1;
/* Marker segment */
static gint hf_marker_segment = -1;
static gint hf_len = -1;
/* MARKER_APP0 */
static gint hf_identifier = -1;
/* MARKER_APP0 - JFIF */
static gint hf_version = -1;
static gint hf_version_major = -1;
static gint hf_version_minor = -1;
static gint hf_units = -1;
static gint hf_xdensity = -1;
static gint hf_ydensity = -1;
static gint hf_xthumbnail = -1;
static gint hf_ythumbnail = -1;
static gint hf_rgb = -1;
/* MARKER_APP0 - JFXX */
static gint hf_extension_code = -1;
/* start of Frame */
static gint hf_sof_header = -1;
static gint hf_sof_precision = -1;
static gint hf_sof_lines = -1;
static gint hf_sof_samples_per_line = -1;
static gint hf_sof_nf = -1;
static gint hf_sof_c_i = -1;
static gint hf_sof_h_i = -1;
static gint hf_sof_v_i = -1;
static gint hf_sof_tq_i = -1;

/* Start of Scan */
static gint hf_sos_header = -1;
static gint hf_sos_ns = -1;
static gint hf_sos_cs_j = -1;
static gint hf_sos_td_j = -1;
static gint hf_sos_ta_j = -1;
static gint hf_sos_ss = -1;
static gint hf_sos_se = -1;
static gint hf_sos_ah = -1;
static gint hf_sos_al = -1;

/* Initialize the subtree pointers */
static gint ett_jfif = -1;
static gint ett_marker_segment = -1;
static gint ett_details = -1;


/**************** GIF related declarations and definitions ****************/


/************************** Function prototypes **************************/


static void
dissect_jfif(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);

void
proto_register_jfif(void);



/****************** JFIF protocol dissection functions ******************/

#define ErrorInvalidJFIF "This is not a valid JFIF (JPEG) object"


/*
 * Process a marker segment (with length).
 */
static void
process_marker_segment(proto_tree *tree, tvbuff_t *tvb, guint32 len,
		guint16 marker, const char *marker_name)
{
	proto_item *ti = NULL;
	proto_tree *subtree = NULL;

	if (! tree)
		return;

	ti = proto_tree_add_item(tree, hf_marker_segment,
			tvb, 0, -1, FALSE);
	subtree = proto_item_add_subtree(ti, ett_marker_segment);

	proto_item_append_text(ti, ": %s (0x%04X)", marker_name, marker);
	proto_tree_add_item(subtree, hf_marker, tvb, 0, 2, FALSE);

	proto_tree_add_item(subtree, hf_len, tvb, 2, 2, FALSE);

	proto_tree_add_text(subtree, tvb, 4, -1,
			"Remaining segment data (%u bytes)", len - 2);
}

/*
 * Process a Start of Frame header (with length).
 */
static void
process_sof_header(proto_tree *tree, tvbuff_t *tvb, guint32 len _U_,
		guint16 marker, const char *marker_name)
{
	proto_item *ti = NULL;
	proto_tree *subtree = NULL;

	if (! tree)
		return;

	ti = proto_tree_add_item(tree, hf_sof_header,
			tvb, 0, -1, FALSE);
	subtree = proto_item_add_subtree(ti, ett_marker_segment);

	proto_item_append_text(ti, ": %s (0x%04X)", marker_name, marker);
	proto_tree_add_item(subtree, hf_marker, tvb, 0, 2, FALSE);

	proto_tree_add_item(subtree, hf_len, tvb, 2, 2, FALSE);

	proto_tree_add_item(subtree, hf_sof_precision, tvb, 4, 1, FALSE);

	proto_tree_add_item(subtree, hf_sof_lines, tvb, 5, 2, FALSE);

	proto_tree_add_item(subtree, hf_sof_samples_per_line, tvb, 7, 2, FALSE);

	proto_tree_add_item(subtree, hf_sof_nf, tvb, 9, 1, FALSE);
	{
		guint8 count = tvb_get_guint8(tvb, 9);
		guint32 offset = 10;
		while (count > 0) {
			proto_tree_add_item(subtree, hf_sof_c_i, tvb, offset++, 1, FALSE);
			proto_tree_add_item(subtree, hf_sof_h_i, tvb, offset, 1, FALSE);
			proto_tree_add_item(subtree, hf_sof_v_i, tvb, offset++, 1, FALSE);
			proto_tree_add_item(subtree, hf_sof_tq_i, tvb, offset++, 1, FALSE);
			count--;
		}
	}
}

/*
 * Process a Start of Segment header (with length).
 */
static void
process_sos_header(proto_tree *tree, tvbuff_t *tvb, guint32 len _U_,
		guint16 marker, const char *marker_name)
{
	proto_item *ti = NULL;
	proto_tree *subtree = NULL;
	guint32 offset;

	if (! tree)
		return;

	ti = proto_tree_add_item(tree, hf_sos_header,
			tvb, 0, -1, FALSE);
	subtree = proto_item_add_subtree(ti, ett_marker_segment);

	proto_item_append_text(ti, ": %s (0x%04X)", marker_name, marker);
	proto_tree_add_item(subtree, hf_marker, tvb, 0, 2, FALSE);

	proto_tree_add_item(subtree, hf_len, tvb, 2, 2, FALSE);

	proto_tree_add_item(subtree, hf_sos_ns, tvb, 4, 1, FALSE);
	{
		guint8 count = tvb_get_guint8(tvb, 4);
		offset = 5;
		while (count > 0) {
			proto_tree_add_item(subtree, hf_sos_cs_j, tvb, offset++, 1, FALSE);
			proto_tree_add_item(subtree, hf_sos_td_j, tvb, offset, 1, FALSE);
			proto_tree_add_item(subtree, hf_sos_ta_j, tvb, offset++, 1, FALSE);
			count--;
		}
	}
	
	proto_tree_add_item(subtree, hf_sos_ss, tvb, offset++, 1, FALSE);
	proto_tree_add_item(subtree, hf_sos_se, tvb, offset++, 1, FALSE);

	proto_tree_add_item(subtree, hf_sos_ah, tvb, offset, 1, FALSE);
	proto_tree_add_item(subtree, hf_sos_al, tvb, offset++, 1, FALSE);
}

/* Process an APP0 block.
 *
 * XXX - This code only works on US-ASCII systems!!!
 */
static void
process_app0_segment(proto_tree *tree, tvbuff_t *tvb, guint32 len,
		guint16 marker, const char *marker_name)
{
	proto_item *ti = NULL;
	proto_tree *subtree = NULL;
	proto_tree *subtree_details = NULL;
	guint32 offset;
	char *str;
	gint str_size;

	if (!tree)
		return;

	ti = proto_tree_add_item(tree, hf_marker_segment,
			tvb, 0, -1, FALSE);
	subtree = proto_item_add_subtree(ti, ett_marker_segment);

	proto_item_append_text(ti, ": %s (0x%04X)", marker_name, marker);
	proto_tree_add_item(subtree, hf_marker, tvb, 0, 2, FALSE);

	proto_tree_add_item(subtree, hf_len, tvb, 2, 2, FALSE);

	str = tvb_get_ephemeral_stringz(tvb, 4, &str_size);
	ti = proto_tree_add_item(subtree, hf_identifier, tvb, 4, str_size, FALSE);
	if (strcmp(str, "JFIF") == 0) {
		/* Version */
		ti = proto_tree_add_none_format(subtree, hf_version,
				tvb, 9, 2, "Version: %u.%u",
				tvb_get_guint8(tvb, 9),
				tvb_get_guint8(tvb, 10));
		subtree_details = proto_item_add_subtree(ti, ett_details);
		proto_tree_add_item(subtree_details, hf_version_major,
				tvb, 9, 1, FALSE);
		proto_tree_add_item(subtree_details, hf_version_minor,
				tvb, 10, 1, FALSE);

		proto_tree_add_item(subtree, hf_units,
				tvb, 11, 1, FALSE);

		/* Aspect ratio */
		proto_tree_add_item(subtree, hf_xdensity,
				tvb, 12, 2, FALSE);
		proto_tree_add_item(subtree, hf_ydensity,
				tvb, 14, 2, FALSE);

		/* Thumbnail */
		proto_tree_add_item(subtree, hf_xthumbnail,
				tvb, 16, 1, FALSE);
		proto_tree_add_item(subtree, hf_ythumbnail,
				tvb, 17, 1, FALSE);
		{
			guint16 x = tvb_get_guint8(tvb, 16);
			guint16 y = tvb_get_guint8(tvb, 17);
			if (x || y) {
				proto_tree_add_item(subtree, hf_rgb,
						tvb, 18, 3 * (x * y), FALSE);
				offset = 18 + (3 * (x * y));
			} else {
				offset = 18;
			}
		}
	} else if (strcmp(str, "JFXX") == 0) {
		proto_tree_add_item(subtree, hf_extension_code,
				tvb, 9, 1, FALSE);
		{
			guint8 code = tvb_get_guint8(tvb, 9);
			switch (code) {
				case 0x10: /* Thumbnail coded using JPEG */
					break;
				case 0x11: /* thumbnail stored using 1 byte per pixel */
					break;
				case 0x13: /* thumbnail stored using 3 bytes per pixel */
					break;
				default: /* Error */
					break;
			}
		}
	} else { /* Unknown */
		proto_item_append_text(ti, " (unknown identifier)");
		offset = 4 + str_size;

		proto_tree_add_text(subtree, tvb, offset, -1,
				"Remaining segment data (%u bytes)", len - 2 - str_size);
	}
	return;
}

/* Process an APP1 block.
 *
 * XXX - This code only works on US-ASCII systems!!!
 */
static void
process_app1_segment(proto_tree *tree, tvbuff_t *tvb, guint32 len,
		guint16 marker, const char *marker_name)
{
	proto_item *ti = NULL;
	proto_tree *subtree = NULL;
	char *str;
	gint str_size;
	int offset = 0;
	int tiff_start;

	if (!tree)
		return;

	ti = proto_tree_add_item(tree, hf_marker_segment,
			tvb, 0, -1, FALSE);
	subtree = proto_item_add_subtree(ti, ett_marker_segment);

	proto_item_append_text(ti, ": %s (0x%04X)", marker_name, marker);
	proto_tree_add_item(subtree, hf_marker, tvb, offset, 2, FALSE);
	offset += 2;

	proto_tree_add_item(subtree, hf_len, tvb, offset, 2, FALSE);
	offset += 2;

	str = tvb_get_ephemeral_stringz(tvb, offset, &str_size);
	ti = proto_tree_add_item(subtree, hf_identifier, tvb, offset, str_size, FALSE);
	offset += str_size;
	if (strcmp(str, "Exif") == 0) {
		/*
		 * Endianness
		 */
		gboolean is_little_endian;
		guint16 val_16;
		guint32 val_32;
		guint16 num_fields;

		offset++; /* Skip a byte supposed to be 0x00 */

		tiff_start = offset;
		val_16 = tvb_get_ntohs(tvb, offset);
		if (val_16 == 0x4949) {
			is_little_endian = TRUE;
			proto_tree_add_text(subtree, tvb, offset, 2, "Endianness: little endian");
		} else if (val_16 == 0x4D4D) {
			is_little_endian = FALSE;
			proto_tree_add_text(subtree, tvb, offset, 2, "Endianness: big endian");
		} else {
			/* Error: invalid endianness encoding */
			proto_tree_add_text(subtree, tvb, offset, 2,
					"Incorrect endianness encoding - skipping the remainder of this application marker");
			return;
		}
		offset += 2;
		/*
		 * Fixed value 42 = 0x002a
		 */
		offset += 2;
		/*
		 * Offset to IFD
		 */
		if (is_little_endian) {
			val_32 = tvb_get_letohl(tvb, offset);
		} else {
			val_32 = tvb_get_ntohl(tvb, offset);
		}
		/*
		 * Check for a bogus val_32 value.
		 * XXX - bogus value message should also deal with a
		 * value that's too large and causes an overflow.
		 * Or should it just check against the segment length,
		 * which is 16 bits?
		 */
		if (val_32 + tiff_start < (guint32)offset + 4) {
			proto_tree_add_text(subtree, tvb, offset, 4,
			    "Start offset of IFD starting from the TIFF header start: %u bytes (bogus, should be >= %u",
			    val_32, offset + 4 - tiff_start);
			return;
		}
		proto_tree_add_text(subtree, tvb, offset, 4,
		    "Start offset of IFD starting from the TIFF header start: %u bytes",
		    val_32);
		offset += 4;
		/*
		 * Skip the following portion
		 */
		if (val_32 + tiff_start > (guint32)offset) {
			proto_tree_add_text(subtree, tvb, offset, val_32 + tiff_start - offset,
			    "Skipped data between end of TIFF header and start of IFD (%u bytes)",
			    val_32 + tiff_start - offset);
		}
		for (;;) {
			offset = val_32 + tiff_start;
			/*
			 * Process the IFD
			 */
			if (is_little_endian) {
				num_fields = tvb_get_letohs(tvb, offset);
			} else {
				num_fields = tvb_get_ntohs(tvb, offset);
			}
			proto_tree_add_text(subtree, tvb, offset, 2, "Number of fields in this IFD: %u", num_fields);
			offset += 2;
			while (num_fields-- > 0) {
				guint16 tag, type;
				guint32 count, off;

				if (is_little_endian) {
					tag = tvb_get_letohs(tvb, offset);
					type = tvb_get_letohs(tvb, offset + 2);
					count = tvb_get_letohl(tvb, offset + 4);
					off = tvb_get_letohl(tvb, offset + 8);
				} else {
					tag = tvb_get_ntohs(tvb, offset);
					type = tvb_get_ntohs(tvb, offset + 2);
					count = tvb_get_ntohl(tvb, offset + 4);
					off = tvb_get_ntohl(tvb, offset + 8);
				}
				/* TODO - refine this */
				proto_tree_add_text(subtree, tvb, offset, 2,
				    "Exif Tag: 0x%04X (%s), Type: %u (%s), Count: %u, "
				    "Value offset from start of TIFF header: %u",
				    tag, val_to_str(tag, vals_exif_tags, "Unknown Exif tag"),
				    type, val_to_str(type, vals_exif_types, "Unknown Exif type"),
				    count, off);
				offset += 12;
			}
			/*
			 * Offset to the next IFD
			 */
			if (is_little_endian) {
				val_32 = tvb_get_letohl(tvb, offset);
			} else {
				val_32 = tvb_get_ntohl(tvb, offset);
			}
			if (val_32 != 0 &&
			    val_32 + tiff_start < (guint32)offset + 4) {
				proto_tree_add_text(subtree, tvb, offset, 4,
				    "Offset to next IFD from start of TIFF header: %u bytes (bogus, should be >= %u)",
				    val_32, offset + 4 - tiff_start);
				return;
			}
			proto_tree_add_text(subtree, tvb, offset, 4,
			    "Offset to next IFD from start of TIFF header: %u bytes",
			    val_32);
			offset += 4;
			if (val_32 == 0)
				break;
		}
	} else {
		proto_tree_add_text(subtree, tvb, offset, -1,
				"Remaining segment data (%u bytes)", len - 2 - str_size);
		proto_item_append_text(ti, " (Unknown identifier)");
	}
}

/* Process an APP2 block.
 *
 * XXX - This code only works on US-ASCII systems!!!
 */
static void
process_app2_segment(proto_tree *tree, tvbuff_t *tvb, guint32 len,
		guint16 marker, const char *marker_name)
{
	proto_item *ti = NULL;
	proto_tree *subtree = NULL;
	char *str;
	gint str_size;

	if (!tree)
		return;

	ti = proto_tree_add_item(tree, hf_marker_segment,
			tvb, 0, -1, FALSE);
	subtree = proto_item_add_subtree(ti, ett_marker_segment);

	proto_item_append_text(ti, ": %s (0x%04X)", marker_name, marker);
	proto_tree_add_item(subtree, hf_marker, tvb, 0, 2, FALSE);

	proto_tree_add_item(subtree, hf_len, tvb, 2, 2, FALSE);

	str = tvb_get_ephemeral_stringz(tvb, 4, &str_size);
	ti = proto_tree_add_item(subtree, hf_identifier, tvb, 4, str_size, FALSE);
	if (strcmp(str, "FPXR") == 0) {
		proto_tree_add_text(tree, tvb, 0, -1, "Exif FlashPix APP2 application marker");
	} else {
		proto_tree_add_text(subtree, tvb, 4 + str_size, -1,
				"Remaining segment data (%u bytes)", len - 2 - str_size);
		proto_item_append_text(ti, " (Unknown identifier)");
	}
}

static void
dissect_jfif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
{
	proto_tree *subtree = NULL;
	proto_item *ti;
	guint tvb_len = tvb_reported_length(tvb);
	guint32 offset = 0;
	tvbuff_t *tmp_tvb;
	guint32 len;
	guint16 marker;

	/* Add summary to INFO column if it is enabled */
	if (check_col(pinfo->cinfo, COL_INFO))
		col_append_sep_fstr(pinfo->cinfo, COL_INFO, " ", "(JPEG JFIF image)");

	if (tree) {
		ti = proto_tree_add_item(tree, proto_jfif,
				tvb, 0, -1, FALSE);
		subtree = proto_item_add_subtree(ti, ett_jfif);
	}

	marker = tvb_get_ntohs(tvb, 0);
	if (marker != MARKER_SOI) {
		if (tree) {
			proto_tree_add_text(subtree, tvb, 0, 2, ErrorInvalidJFIF);
			return;
		}
	}
	if (tree)
		proto_tree_add_item(subtree, hf_marker, tvb, 0, 2, FALSE);

	offset = 2;

	/*
	 * Process the remaining markers and marker segments
	 */
	while (offset < tvb_len) {
		const char *str;
		marker = tvb_get_ntohs(tvb, offset);
		str = match_strval(marker, vals_marker);
		if (str) { /* Known marker */
			if (marker_has_length(marker)) { /* Marker segment */
				/* Length of marker segment = 2 + len */
				len = tvb_get_ntohs(tvb, offset + 2);
				tmp_tvb = tvb_new_subset(tvb, offset, 2 + len, 2 + len);
				switch (marker) {
					case MARKER_APP0:
						process_app0_segment(subtree, tmp_tvb, len, marker, str);
						break;
					case MARKER_APP1:
						process_app1_segment(subtree, tmp_tvb, len, marker, str);
						break;
					case MARKER_APP2:
						process_app2_segment(subtree, tmp_tvb, len, marker, str);
						break;
					case MARKER_SOF0:
					case MARKER_SOF1:
					case MARKER_SOF2:
					case MARKER_SOF3:
					case MARKER_SOF5:
					case MARKER_SOF6:
					case MARKER_SOF7:
					case MARKER_SOF8:
					case MARKER_SOF9:
					case MARKER_SOF10:
					case MARKER_SOF11:
					case MARKER_SOF13:
					case MARKER_SOF14:
					case MARKER_SOF15:
						process_sof_header(subtree, tmp_tvb, len, marker, str);
						break;
					case MARKER_SOS:
						process_sos_header(subtree, tmp_tvb, len, marker, str);
						/*
						 * TODO - dissect a scan; the scan data is encoded.
						 */
						proto_tree_add_text(subtree, tvb, offset + 2 + len, -1,
								"JFIF dissection stops here (dissection of a scan is not yet implemented)");
						return;
						break;
					default:
						process_marker_segment(subtree, tmp_tvb, len, marker, str);
						break;
				}
				offset += 2 + len;
			} else { /* Marker but no segment */
				/* Length = 2 */
				proto_tree_add_item(subtree, hf_marker,
						tvb, offset, 2, FALSE);
				offset += 2;
			}
		} else { /* Reserved! */
			ti = proto_tree_add_item(subtree, hf_marker,
					tvb, offset, 2, FALSE);
			proto_item_append_text(ti, " (Reserved)");
			return;
		}
	}

	return;
}


/****************** Register the protocol with Wireshark ******************/


/* This format is required because a script is used to build the C function
 * that calls the protocol registration. */

void
proto_register_jfif(void)
{
	/*
	 * Setup list of header fields.
	 */
	static hf_register_info hf[] = {
		/* Marker */
		{ &hf_marker,
			{	"Marker",
				IMG_JFIF ".marker",
				FT_UINT8, BASE_HEX, VALS(vals_marker), 0x00,
				"JFIF Marker",
				HFILL
			}
		},
		/* Marker segment */
		{ &hf_marker_segment,
			{	"Marker segment",
				IMG_JFIF "marker_segment",
				FT_NONE, BASE_NONE, NULL, 0x00,
				"Marker segment",
				HFILL
			}
		},
		{ &hf_len,
			{	"Length",
				IMG_JFIF ".length",
				FT_UINT16, BASE_DEC, 0, 0x00,
				"Length of segment (including length field)",
				HFILL
			}
		},
		/* MARKER_APP0 */
		{ &hf_identifier,
			{	"Identifier",
				IMG_JFIF ".identifier",
				FT_STRINGZ, BASE_NONE, NULL, 0x00,
				"Identifier of the segment",
				HFILL
			}
		},
		/* MARKER_APP0 - JFIF */
		{ &hf_version,
			{	"Version",
				IMG_JFIF ".version",
				FT_NONE, BASE_NONE, NULL, 0x00,
				"JFIF Version",
				HFILL
			}
		},
		{ &hf_version_major,
			{	"Major Version",
				IMG_JFIF ".version.major",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"JFIF Major Version",
				HFILL
			}
		},
		{ &hf_version_minor,
			{	"Minor Version",
				IMG_JFIF ".version.minor",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"JFIF Minor Version",
				HFILL
			}
		},
		{ &hf_units,
			{	"Units",
				IMG_JFIF ".units",
				FT_UINT8, BASE_DEC, VALS(vals_units), 0x00,
				"Units used in this segment",
				HFILL
			}
		},
		{ &hf_xdensity,
			{	"Xdensity",
				IMG_JFIF ".Xdensity",
				FT_UINT16, BASE_DEC, NULL, 0x00,
				"Horizontal pixel density",
				HFILL
			}
		},
		{ &hf_ydensity,
			{	"Ydensity",
				IMG_JFIF ".Ydensity",
				FT_UINT16, BASE_DEC, NULL, 0x00,
				"Vertical pixel density",
				HFILL
			}
		},
		{ &hf_xthumbnail,
			{	"Xthumbnail",
				IMG_JFIF ".Xthumbnail",
				FT_UINT16, BASE_DEC, NULL, 0x00,
				"Thumbnail horizontal pixel count",
				HFILL
			}
		},
		{ &hf_ythumbnail,
			{	"Ythumbnail",
				IMG_JFIF ".Ythumbnail",
				FT_UINT16, BASE_DEC, NULL, 0x00,
				"Thumbnail vertical pixel count",
				HFILL
			}
		},
		{ &hf_rgb,
			{	"RGB values of thumbnail pixels",
				IMG_JFIF ".RGB",
				FT_BYTES, BASE_NONE, NULL, 0x00,
				"RGB values of the thumbnail pixels (24 bit per pixel, Xthumbnail x Ythumbnail pixels)",
				HFILL
			}
		},
		/* MARKER_APP0 - JFXX */
		{ &hf_extension_code,
			{	"Extension code",
				IMG_JFIF ".extension.code",
				FT_UINT8, BASE_HEX, VALS(vals_extension_code), 0x00,
				"JFXX extension code for thumbnail encoding",
				HFILL
			}
		},
		/* Header: Start of Frame (MARKER_SOF) */
		{ &hf_sof_header,
			{	"Start of Frame header",
				IMG_JFIF ".sof",
				FT_NONE, BASE_NONE, NULL, 0x00,
				"Start of Frame header",
				HFILL
			}
		},
		{ &hf_sof_precision,
			{	"Sample Precision (bits)",
				IMG_JFIF ".sof.precision",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"Specifies the precision in bits for the samples of the components in the frame.",
				HFILL
			}
		},
		{ &hf_sof_lines,
			{	"Lines",
				IMG_JFIF ".sof.lines",
				FT_UINT16, BASE_DEC, NULL, 0x00,
				"Specifies the maximum number of lines in the source image.",
				HFILL
			}
		},
		{ &hf_sof_samples_per_line,
			{	"Samples per line",
				IMG_JFIF ".sof.samples_per_line",
				FT_UINT16, BASE_DEC, NULL, 0x00,
				"Specifies the maximum number of samples per line in the source image.",
				HFILL
			}
		},
		{ &hf_sof_nf,
			{	"Number of image components in frame",
				IMG_JFIF ".sof.nf",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"Specifies the number of source image components in the frame.",
				HFILL
			}
		},
		{ &hf_sof_c_i,
			{	"Component identifier",
				IMG_JFIF ".sof.c_i",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"Assigns a unique label to the ith component in the sequence "
				"of frame component specification parameters.",
				HFILL
			}
		},
		{ &hf_sof_h_i,
			{	"Horizontal sampling factor",
				IMG_JFIF ".sof.h_i",
				FT_UINT8, BASE_DEC, NULL, 0xF0,
				"Specifies the relationship between the component horizontal "
				"dimension and maximum image dimension X.",
				HFILL
			}
		},
		{ &hf_sof_v_i,
			{	"Vertical sampling factor",
				IMG_JFIF ".sof.v_i",
				FT_UINT8, BASE_DEC, NULL, 0x0F,
				"Specifies the relationship between the component vertical "
				"dimension and maximum image dimension Y.",				
				HFILL
			}
		},
		{ &hf_sof_tq_i,
			{	"Quantization table destination selector",
				IMG_JFIF ".sof.tq_i",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"Specifies one of four possible quantization table "
				"destinations from which the quantization table to use "
				"for dequantization of DCT coefficients of component Ci "
				"is retrieved.",
				HFILL
			}
		},

		/* Header: Start of Segment (MARKER_SOS) */
		{ &hf_sos_header,
			{	"Start of Segment header",
				IMG_JFIF ".header.sos",
				FT_NONE, BASE_NONE, NULL, 0x00,
				"Start of Segment header",
				HFILL
			}
		},
		{ &hf_sos_ns,
			{	"Number of image components in scan",
				IMG_JFIF ".sos.ns",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"Specifies the number of source image components in the scan.",
				HFILL
			}
		},
		{ &hf_sos_cs_j,
			{	"Scan component selector",
				IMG_JFIF ".sos.component_selector",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"Selects which of the Nf image components specified in the "
				"frame parameters shall be the jth component in the scan.",
				HFILL
			}
		},
		{ &hf_sos_td_j,
			{	"DC entropy coding table destination selector",
				IMG_JFIF ".sos.dc_entropy_selector",
				FT_UINT8, BASE_DEC, NULL, 0xF0,
				"Specifies one of four possible DC entropy coding table "
				"destinations from which the entropy table needed "
				"for decoding of the DC coefficients of component Csj "
				"is retrieved.",
				HFILL
			}
		},
		{ &hf_sos_ta_j,
			{	"AC entropy coding table destination selector",
				IMG_JFIF ".sos.ac_entropy_selector",
				FT_UINT8, BASE_DEC, NULL, 0x0F,
				"Specifies one of four possible AC entropy coding table "
				"destinations from which the entropy table needed "
				"for decoding of the AC coefficients of component Csj "
				"is retrieved.",
				HFILL
			}
		},
		{ &hf_sos_ss,
			{	"Start of spectral or predictor selection",
				IMG_JFIF ".sos.ss",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"In the DCT modes of operation, this parameter specifies the "
				"first DCT coefficient in each block in zig-zag order which "
				"shall be coded in the scan. This parameter shall be set to "
				"zero for the sequential DCT processes. "
				"In the lossless mode of operations this parameter is used "
				"to select the predictor.",
				HFILL
			}
		},
		{ &hf_sos_se,
			{	"End of spectral selection",
				IMG_JFIF ".sos.se",
				FT_UINT8, BASE_DEC, NULL, 0x00,
				"Specifies the last DCT coefficient in each block in zig-zag "
				"order which shall be coded in the scan. This parameter shall "
				"be set to 63 for the sequential DCT processes. "
				"In the lossless mode of operations this parameter has no "
				"meaning. It shall be set to zero.",
				HFILL
			}
		},
		{ &hf_sos_ah,
			{	"Successive approximation bit position high",
				IMG_JFIF ".sos.ah",
				FT_UINT8, BASE_DEC, NULL, 0xF0,
				"This parameter specifies the point transform used in the "
				"preceding scan (i.e. successive approximation bit position "
				"low in the preceding scan) for the band of coefficients "
				"specified by Ss and Se. This parameter shall be set to zero "
				"for the first scan of each band of coefficients. "
				"In the lossless mode of operations this parameter has no "
				"meaning. It shall be set to zero.",
				HFILL
			}
		},
		{ &hf_sos_al, 
			{	"Successive approximation bit position low or point transform",
				IMG_JFIF ".sos.al",
				FT_UINT8, BASE_DEC, NULL, 0x0F,
				"In the DCT modes of operation this parameter specifies the "
				"point transform, i.e. bit position low, used before coding "
				"the band of coefficients specified by Ss and Se. "
				"This parameter shall be set to zero for the sequential DCT "
				"processes. In the lossless mode of operations, this "
				"parameter specifies the point transform, Pt.",
				HFILL
			}
		},
	};

	/* Setup protocol subtree array */
	static gint *ett[] = {
		&ett_jfif,
		&ett_marker_segment,
		&ett_details,
	};

	/* Register the protocol name and description */
	proto_jfif = proto_register_protocol(
			"JPEG File Interchange Format",
			"JFIF (JPEG) image",
			IMG_JFIF
	);

	/* Required function calls to register the header fields
	 * and subtrees used */
	proto_register_field_array(proto_jfif, hf, array_length(hf));
	proto_register_subtree_array(ett, array_length(ett));

	register_dissector("image-jfif", dissect_jfif, proto_jfif);
}


void
proto_reg_handoff_jfif(void)
{
	dissector_handle_t jfif_handle;

	jfif_handle = find_dissector("image-jfif");

	/* Register the JPEG media type */
	dissector_add_string("media_type", "image/jfif", jfif_handle);
	dissector_add_string("media_type", "image/jpg", jfif_handle);
	dissector_add_string("media_type", "image/jpeg", jfif_handle);
}
